Abstract : High pressure triaxial-permeability equipment was developed to study the compressibility and permeability behavior of compacted untreated and stabilized soils at confining pressures up to 70 kg/sq cm under back pressures up to 15 kg/sq cm. Permeabilities down to 10 to the minus 10 power cm/sec can be measured using cylindrical test specimens 8 cm long and 10 sq cm cross-sectional area. This equipment has been used to study the influence of cement stabilization, molding water content, and type of compaction on the compressibility and permeability behavior of Massachusetts clayey silt (M-21). The results of this investigation show: (1) Both molding water content and type of compaction influence the degree of cracking that occurs during unsealed hot curing of M-21 plus 5% cement; (2) Sealing during curing eliminates cracking; (3) Cracking causes an increase in the permeability and compressibility of the stabilized soil at consolidation pressures up to 50 kg/sq cm; (4) Provided cracking during curing is prevented, the stabilized soil shows a much larger decrease in permeability with increasing molding water content than does the untreated soil. Further, kneading compaction results in a lower permeability than static compaction at molding water contents around optimum for the stabilized soil; (5) The permeability of the stabilized soil decreases with increasing curing time and increasing time of permeation.